impossible to install java

Hi,

for some reason I uninstalled my old 6.x JRE, and installed the latest one, 7u4.
ever since then none of my browsers, neither firefox nor opera can find java.
I reinstalled the JRE at least 4 times, but nothing changed. I am not a java expert,
(actually hate it), but I don't think that this situation would be something odd.
in the java control panel/advanced tab under default java branch I can not check
in the "Mozilla family" persistently, as it remains unchecked when I open it next time.

If I go to the java.com test page, it says "An old version of Java has
been detected on your system."